Touch control circuit



May 7, 1968 c. E. ATKINS TOUCH CONTROL CIRCUIT Filed 001;. 21, 1966 INVENTOR 7E 4 m 5 m A wm w United States Patent 3,382,408 TOUCH CONTROL CIRCUIT Carl E. Atkins, Montclair, N.J., assignor, by mesne assignments, to Wagner Electric Corporation, South Bend, lnd., a corporation of Delaware Filed Oct. 21, 1966, Ser. No. 588,457 4 Claims. (Cl. 315-362) This invention relates to a touch control circuit which lights lamp when the lamp container is held in the hand of the operator. The invention has particular reference to :a dental mirror having a small electric lamp in the handle but the control circuit can be used in many other applications.

Lamps for use with dental mirrors are old in the art. A small lamp is positioned at one end of the handle and the light from the lamp is directed through the handle by a cylinder of glass or plastic. At the exit end, the light is reflected by the mirror to whatever object the operator is Working on and illumination is thereby provided for portions of the mouth, or other cavities, that normally are difficult to observe. One of the main objections to such an arrangement is the fact that the mirror handle gets hot when put to one side. This objection has been eliminated by the control circuit which turns the lamp out when the mirror is not held in the hand. Normally, such a control circuit would be subjected to outside interference such as the noise generated by a dentists drill motor. This interference has been substantially eliminated by special circuitry which will be described in detail later.

One of the objects of this invention is to provide an improved touch control circuit which avoids one or more of the disadvantages and limitations of prior art control circuits.

Another object of the invention is to provide a circuit which is substantially unaffected by high frequency noise due to stray electrostatic and electromagnetic fields which may be caused by motors and other electrical equipment.

Another object of the invention is to eliminate overheating of the handle of a mirror or tool housing an illuminating lamp.

Another object of the invention is to increase the life of the lamp installed in a handle by turning it off when not in use.

Another object of the invention is to provide a touch control circuit which is light in weight, small, and consumes little power for its operation.

The invention comprises an oscillator which applies a signal to its output circuit only when a handle containing a lamp is held in the hand. Amplifying means are connected to the oscillator for amplifying the oscillator signal. A switch circuit is coupled to the amplifying means for passing current when the amplifying means produces a signal. A relay is connected across the switch circuit and lights the lamp whenever the switch circuit passes current.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawing.

FIG. 1 is a cross sectional view of a dental mirror with a handle, an illuminating lamp, and a light conveying cylinder of transparent material in the handle.

FIG. 2 is a schematic wiring diagram of connections of a control circuit coupled between a source of alternating current power, the handle, and the lamp.

FIG. 3 is a cross sectional view, to an enlarged scale, of the dental mirror handle shown in FIG. 1 and is taken along line 33 of that figure.

Referring now to FIGS. 1 and 3, the dental mirror includes a hollow handle made of conductive material. The hollow portion of the handle is filled by a transparent 3,382,468 Patented May 7, 1968 material 11 which may be Lucite, glass, or any other suitable material. A small circular mirror 12 is mounted on a metal backing 13 and both are held by a rod 14 secured to the handle 10 by a socket 15. At the other end of the handle 10 an enlarged portion 16 holds a small lamp 17 mounted in a socket 18 and connected to a source of alteranting current power by conductors 20. The lamp socket may be secured to the portion 16 by any convenient means.

The control circuit shown in FIG. 2 includes an oscillator having a neon lamp 21 as the non-linear element. A direct current supply for the lamp is derived from an alternating current power supply which is to be connected to terminals 22 and 23. The direct current is produced by the rectifying action of a diode 24, resistor 25-, and shunt capacitor 26. The oscillating circuit includes a series resistor 27, the lamp 2 1, and a shunt circuit which includes capacitor 28 and a resistor 30*. A capacitor 33 is connected to the handle 10 and the junction of resistor 27 with tube 21. An adjustable resistor 31 is connected between one of the lamp terminals and the ground connection 32 which forms the other conductor connected to terminal 23. The operation of this oscillator is already known as it has been described and claimed in U.S. Patent 3,199,033. The current flowing through resistor 27 charges capacitors 28 and 33 until the firing voltage of lamp 21 is reached. Then conduction is established in the lamp and the voltage drops to and below the current sustaining voltage. The capacitors repeatedly charge to the firing voltage and then discharge producing current pulses through the lamp. Each time the lamp fires the discharge of capacitor 28 is through the lamp and resistor 30 and the discharge of capacitor 33 and the distributed capacity 33' between the handle 10 and ground indicated in dotted lines in the drawing is through the lamp 21 and resistor 31. It should be obvious that the discharge current pulses flowing through resistor 30* move in one direction while the discharge current pulses through resistor 31 move in the opposite direction and if resistors 30 and 31 are properly adjusted, there will be no output signal applied across the base and emitter electrodes of transistor 34. This is the normal condition when the handle 16 is not held in the operators hand.

Transistor 34 is coupled to a second transistor 35 which also serves as an amplifier. The coupling circuit includes a series capacitor 36 and a parallel capacitor 37 Which is designed to short circuit all the higher alternating current pulses which include most of the noise pulses picked up by the circuit due to external electromagnetic and electrostatic fields. Both transistors 34 and 35 are biased for normal amplification by resistors 38 and 39, each connected respectively between the base and the collector of transistors 34 and 35. Capacitor 37 is quite small and affects the amplification ratio by only a small amount.

The output of transistor 35 is coupled to a switching circuit 40 in series with another capacitor 40". The switching circuit 40 is composed of an NPN transistor 41 and a PNP transistor 42 with the base of each transistor connected to the collector of the other transistor. The output of transistor 35 is connected through capacitor 40' to the base electrode of transistor 42 while the emitters of transistors 4 1 and 42 are connected respectively in series with resistors 43 and 44 across the alternating current supply.

The combination of transistors 41 and 421 form an electronic switch which is normally non-conductive because of the positive bias on the base of transistor 42. The positive bias for the base is obtained from the positive half cycles which send current pulses through the transistors and build up a charge on capacitor 45 to about 6 volts, the Zener breakdown voltage. When negative pulses are applied to the base of transistor 42 from the collector of transistor 35, transistor 42 is made conductive and thereby causes a base current to flow in transistor 41 and thereby causes conduction in transistor 41. Conduction of transistor 41 increases the negative potential on the base of. transistor 42 and thereby increases conduction of that element. The switch circuit 40 may be replaced by a silicon controlled rectifier or by a three-terminal four-zone semiconductor device.

The switching circuit 40 is shunted by a winding 46 .of a relay 46 having a pair of contacts 47. Winding 46 is connected in series with a diode 48 so that it receives only negative voltage for its operation. A large capacitor 50 is connected across the winding 46 to maintain the relay energized during the positive half cycles of the voltage wave and to prevent chattering of the relay contacts. The upper contact .of the pair 47 is connected in series with a primary winding 51 of a transformer 52, the secondary winding 53 being connected :by conductors 20 to lamp 17. The other end of winding 51 is connected to terminal 22.

The operation of this circuit is as follows: Under normal conditions when the handle L10 is lying on a table, and there is very little capacity to ground, the oscillator circuit produces two currents as described above, one moving in resistor 30 and the other moving in an opposite direction in resistor 31. These currents balance each other and produce substantially no output applied to amplifying transistor 34. Under these conditions the double transistor switch 40 is non-conductive and current flows from supply terminal 22 through resistor 43, diode 48, and winding 46, to the other supply terminal 23. This current actuates the relay and opens contacts 47 cutting otf current to the primary winding 51 and providing no current for lamp 17. Now, when the operator touches handle 10, the capacity 33' to ground is increased many times and the output currents from the oscillator circuit are unbalanced, thereby providing a considerable output to amplifier stages 34 and 35 and causing conduction in the switch combination 40. This action takes place each time a negative cycle is applied to resistor 43. When the switch 40 is made conductive at each negative cycle, no negative pulses flow through diode 48 and winding 46 and thereby the relay armature is released and contacts 47 are closed. During positive half cycles there can be no current applied to relay winding 46 because these pulses are stopped by diode 48. When current flows through contacts 47, a circuit is established from terminal 23, through contacts 47, winding -1, to terminal 22. This current lights the lamp 17 and maintains it in its lighted condition as long as the operator holds the handle in his hand. As soon as the operator puts down the dental mirror, the oscillator circuit is again balanced, the switch 40 is made non-conductive, the relay 46' is again actuated, and the contacts 47 are opened, thereby turning out the light.

While the invention has been described with application to a dental mirror it is .obvious that other types of instruments such as knives, exploring lights, and scissors may use this type of illumination.

The foregoing disclosure and drawing are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

I claim:

1. The combination with a lamp installed in a handle to be held by an operator of a control circuit for the lamp comprising a source of alternating energy, an oscillator coupled to the source for producing control signals, said oscillator being normally balanced to produce a null signal, a capacitor forming one element of the oscillator, and connected to the handle for unbalancing the oscillater to produce output signals when the handle is held by an operator, means for amplifying the oscillator output, an electronic switching device connected to said amplifying means to be rendered conductive upon application of an amplified signal thereto and a relay connected across said switching device to be shunted thereby when said switching device i rendered conductive, said relay controlling energization of the lamp.

2. The combination according to claim 1 wherein said amplifying means include a first amplifier coupled to the oscillator and a second amplifier connected between said first amplifier and said switching device, and wherein a capacitor is connected across the output of said first amplifier to eliminate high frequency noise due to external fields.

3. The combination according to claim 1 including rectifying means coupled between said oscillator and said source and wherein said oscillator includes a non-linear breakdown device, a second capacitor and a first and a second resistor, said capacitors charging from said rectifying means and discharging through said non-linear breakdown device, said first resistor being in the discharge path of said first capacitor and said second resistor being in the discharge path of said second capacitor, the output of the oscillator being taken across said resister and being null when the discharge currents are equal.

4. The combination according to claim 1 wherein said switching device includes two transistors which are made conductive by the application of a negative pulse from the oscillator means.

No references cited.

DAVID J. GALVIN, Primary Examiner. 

1. THE COMBINATION WITH A LAMP INSTALLED IN A HANDLE TO BE HELD BY AN OPERATOR OF A CONTROL CIRCUIT FOR THE LAMP COMPRISING A SOURCE OF ALTERNATING ENERGY, AN OSCILLATOR COUPLED TO THE SOURCE FOR PRODUCING CONTROL SIGNALS, SAID OSCILLATOR BEING NORMALLY BALANCED TO PRODUCE A NULL SIGNAL, A CAPACITOR FORMING ONE ELEMENT OF THE OSCILLATOR, AND CONNECTED TO THE HANDLE FOR UNBALANCING THE OSCILLATOR TO PRODUCE OUTPUT SIGNALS WHEN THE HANDLE IS HELD BY AN OPERATOR, MEANS FOR AMPLIFYING THE OSCILLATOR OUTPUT, AN ELECTRONIC SWITCHING DEVICE CONNECTED TO SAID AMPLIFYING MEANS TO BE RENDERED CONDUCTIVE UPON APPLICATION OF AN AMPLIFIED SIGNAL THERETO AND A RELAY CONNECTED ACROSS SAID SWITCHING DEVICE TO BE SHUNTED THEREBY WHEN SAID SWITCHING DEVICE IS RENDERED CONDUCTIVE, SAID RELAY CONTROLLING ENERGIZATION OF THE LAMP. 